Antilock braking systems are commonly employed in trailers and other towable vehicles to control tire slip. The antilock braking systems use wheel speed monitors to monitor relative deceleration rates of wheels while braking and respond to indications of slip by temporarily reducing the hydraulic pressure to the brakes. Typically, wheel speed monitors used in antilock braking systems have two primary components: a sensor and a tone ring.
The tone ring is a structure such as a ring or disk that has a number of reference points (e.g., notched teeth) on it. The tone ring rotates with the wheel and the reference points are sensed by the sensor to generate data about the speed of the corresponding wheel. Sensors typically are fixedly attached to the brake flange such that a desired gap is maintained between the sensor and the tone ring. In most implementations, the wheel speed monitor only functions properly when the particular gap is maintained. However, any number of events can cause some object to exert force on the sensor, pushing it out of position. Typically, a mechanic must then reposition the sensor to achieve the necessary gap.